The fabrication of a dental restorative, such as a crown or bridge, normally involves building up porcelain or a similar material on a metallic understructure, the latter being necessary to provide strength to the crown or bridge. The porcelain is applied as a wet paste and generally consists of a mixture of porcelain powder and a wetting agent, for example, water. It is necessary to use a paste so that the porcelain can be readily contoured into a toothlike shape. The paste is formed by mixing and stirring the powder and wetting agent in any convenient vessel. The paste after being properly mixed, is transferred by a suitable device (e.g., spatula) from the vessel to the exposed surface of the metallic understructure.
Irregularities in the porcelain can weaken the crown or bridge and cause cracks or other surface imperfections to result. These irregularities may occur due to lumps within the paste or from moisture or air entrapped in the porcelain paste. Furthermore, voids caused by the entrained moisture or air can result in excessive shrinking of the porcelain when it is fired. The paste lumps can be eliminated by more thorough and effective mixing with a spatula or other suitable device.
Conventionally, the voids are eliminated during buildup and shaping of paste on the understructure by a technique known as condensation of the porcelain paste. This technique causes compaction of the porcelain paste on the understructure whereby the entrapped moisture and air percolate to the exposed surface of the applied paste and thus increases the concentration of porcelain powder on the understructure. The condensation technique is normally achieved by vibrating the applied porcelain paste on the understructure.
The porcelain paste is applied to and shaped on the understructure while the latter is supported on a plaster mold of the jaw. It is extremely desirable to condense the paste at this stage while it is being applied and shaped. If condensation is postponed until after the paste is shaped, the settled and compacted porcelain may require major reshaping. However, it has been found that condensation induced by a vibration action at an early stage eliminates an excessive amount of moisture and, thus, prevents proper shaping of the porcelain. Heretofore, the condensation step was normally postponed until the shaping was completed or was limited to tapping the entire plaster mold against the bench top. Such a procedure, however, was time consuming and awkward. In lieu of tapping the whole mold on a bench, effective condensation can be accomplished by utilizing a small mallet; such mallet tapping causes a substantially less severe and more easily controllable condensation of the porcelain. Typically, the dental technologist alternates frequently between applying, shaping, and condensing the porcelain paste on the understructure.
When the porcelain paste has attained the desired shape, the understructure with shaped porcelain thereon is transferred from the plaster mold to a clamp-like holder such as forceps. Generally, condensation is initiated at this point by rubbing a ribbed tool against a portion of the clamp-like device holding the understructure. The paste previously applied to the understructure is not sufficiently hard at this time for the tool to tap the paste directly.
The fabrication of a dental crown or bridge requires the dental technologist's close attention to small details. The frequent alternation between applying and condensing the porcelain paste is particularly demanding on the technologist and conventionally requires the use of different instruments to perform each function and even tapping the plaster mold against a bench top. The need to put one instrument down and then find and pick up a second instrument in rapid succession is difficult and time consuming and often leads to error.